867
FXUS62 KCHS 211339
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
939 AM EDT Fri Jun 21 2024

.SYNOPSIS...
Tropical low pressure will approach the Georgia and northeast
Florida coast late today, then shift inland tonight. High
pressure will then prevail into the middle of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Today: Satellite, radar and reconnaissance data shows tropical
low pressure centered about 130 miles southeast of Sapelo
Island. The low appears to be embedded within a large envelope
of PWATS in excess of 2 inches as noted by the latest GOES-E
Total Precipitable Water product. Near term guidance is pretty
unanimous in bringing the tropical low into the northeast
Florida or far southern Georgia coast later tonight. As the low
draws closer, this envelop of higher moisture will eventually
more onshore later this afternoon bringing a distinct change in
airmass, especially at the coast. Although the dry air will
initially be hard to displace, PWATs are on track to surge later
this afternoon into tonight nearing 2" by late afternoon as the
coast. This increased moisture coupled with diurnal instability
and increased coastal convergence will support an increase in
precipitation this afternoon with scattered showers with a few
tstms possible. Afternoon pops ranging from 20-30% inland (where
drier air will have a greater influence) to 50% over the
coastal counties looks reasonable given current trends. Highs
from the lower 90s well inland to the lower-mid 80s at the
beaches look on track. Breezy to locally windy conditions will
linger along the coastal corridor, especially at the beaches.

Tonight: The remains of the Atlantic low will move into
Southeast Georgia as an open wave. Elevated PWat and continued
coastal convergence will allow for at least isolated to
scattered showers and a few t-storms. The higher PoPs and
greater QPF will be in closer proximity to the remains of the
surface low. There is some evidence of low stratus forming over
our northwest tier late, and perhaps resulting in some patchy
fog. Lows will be a little warmer than recent nights with higher
dew points and more of a southeast synoptic flow.

&&

.SHORT TERM /SATURDAY THROUGH MONDAY/...
Saturday: The mid-levels will consist of broad High pressure over
the Lower MS Valley, and a weak Low just offshore. The Low will
shift towards the Southeast coast and weaken, pushing the High
further to the west. At the surface, a remnant Low may be over or
near our area in the morning. Though, it`s expected to transition
into a trough over the Southeast by the afternoon. Additionally,
High pressure will be over Bermuda. There will be deep moisture
across the region from the remnant Low. PWATs across our area should
exceed 2", which is above the 90% mark for CHS per SPC Sounding
Climatology and nearly 2 standard deviations per NAEFs. Both the
synoptic models and long range CAMs point to an active summertime
pattern. Expect likely POPs across our GA counties in the afternoon,
aided by the sea breeze, and chance POPs across our SC counties.
POPs will decrease in the evening and overnight, but remain in the
chance category along the coast. We can`t completely rule out a
marginally severe thunderstorm with damaging winds. But the bigger
concern will be the potential for locally heavy rainfall underneath
the thunderstorms, especially given the weak steering flow and
potential for training. Highs will be in the upper 80s to lower 90s.
Lows will generally be in the 70s.

Sunday: A weak mid-level Low offshore in the morning will get
absorbed into the overall flow. Meanwhile, troughing will develop
over the East Coast. Surface High pressure will be in the Atlantic
with weak troughing over the Southeast. Deep moisture will persist
across our area with PWATs exceeding 2". This remains well above
normal for this time of year. Another active afternoon is expected
with likely POPs across most of our area. Similar to Saturday, we
can`t completely rule out a marginally severe thunderstorm with
damaging winds. But the bigger concern remains the potential for
locally heavy rainfall underneath the thunderstorms due to the weak
steering flow. The convection will decrease in both coverage and
intensity during the evening and overnight. Highs will range from
the upper 80s at the beaches to the lower to mid 90s elsewhere.
Additionally, heat indices should top the 100 degree mark before
convection develops. Lows will generally be in the mid 70s.

Monday: The mid-levels will consist of a trough over the East Coast,
gradually shifting offshore. At the surface, troughing will be over
the Southeast in the morning, with High pressure in the Atlantic. A
cold front will approach from the north during the day. The deepest
moisture appears to get pushed offshore in advance of the front,
with the 2+" PWATs off our coast. However, PWATs ~1.75" will remain
across our area. The heat may be a bigger concern with rising 850 mb
temperatures and compression ahead of the front. Highs could peak in
the mid to upper 90s, except cooler at the beaches. But dew points
well into the 70s could cause heat indices to rise to 105-110
degrees, which could prompt coastal Heat Advisories. However,
afternoon convection is expected to quickly develop, which would
lower temperatures. This aspect of the forecast will need to be
refined further.

&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
Weak mid-level troughing will occasionally be over the East Coast.
Surface troughing or weak fronts will be impacting the Southeast
U.S. while High pressure is near Bermuda. This summertime pattern
will yield diurnal convection. The forecast generally has POPs
peaking in the afternoon and evening, then gradually transitioning
them to favor the Atlantic coastal waters during the overnight
hours. High temperatures will be well into the 90s. Heat indices
could also rise to 105-110 degrees along the coast, which could
prompt some Heat Advisories.

&&

.AVIATION /14Z FRIDAY THROUGH TUESDAY/...
KCHS/KJZI/KSAV: No concerns through about 15-16Z, then some
showers will start to develop as the tropical disturbance in the
Atlantic gets closer, and the dry air starts to erode.
Eventually the showers will become more scattered in coverage,
with even the risk of a few t-storms. Brief flight restrictions
can certainly occur in any of the convection, but for now we
show VFR weather. The showers and t-storms will decrease in
coverage late day/early evening, but a few could still linger
into tonight as the remnants of the disturbance are found near
the Florida-Georgia border.

All sites will experience gusty easterly winds today, but less
than recent days.

Extended Aviation Outlook: Mostly VFR. However, convection will
bring brief flight restrictions, mainly each afternoon and
evening.

&&

.MARINE...
Today: Tropical low pressure southeast of the Altamaha Sound
will approach the coast this afternoon into tonight. There
remains a decent gradient in place between that system and
elongated high pressure to the north. Enough so that we still
have Small Craft Advisories on all Atlantic waters, for E-NE
winds of 15-20 kt and gusts near 25 kt. Seas are still elevated
after several days of a persistent onshore wind, and are as high
as 6 feet within 20 nm of shore, but up to 8 feet further out.
Charleston Harbor should not have as much wind as recently, but
still up to 15 kt or occasionally 20 kt. Mariners can expect
isolated to scattered t-storms developing today in response to
the tropical system.

Tonight: The tropical low will become an open wave as it moves
into southeast Georgia. The gradient eases, and we will start
to see winds and eventually seas come down enough where we can
drop the Small Craft Advisories.

Saturday through Tuesday: A typical summertime pattern is
expected with High pressure in the Atlantic and occasional
surface troughing over the Southeast. By Sunday, sustained winds
will mainly be from the south or southwest, strongest along the
land/sea interface with the formation of the afternoon sea
breeze. Seas will average 2-4 ft.

Rip Currents: Persistent onshore flow and lingering elevated
seas will again produce a High Risk of rip currents at all
beaches today. Lifeguards continued to indicate hazardous
swimming conditions at area beaches, and these conditions are
expected to continue today. For Saturday, winds will stay
onshore, but seas will trend lower. Therefore, we have a
moderate risk of rip currents for all beaches.

&&

.TIDES/COASTAL FLOODING...
Tide levels will continue to be elevated late this week thanks
to persistent onshore flow and elevated seas. However, the
astronomical tide values aren`t particularly high, which will
reduce the overall coastal flooding risk. The high tide this
evening (~8:30 pm) in Charleston Harbor will likely fall short
of when shallow coastal flooding begins. However, with the
tropical disturbance moving in our general direction, but
staying to the south, this puts the local area in a favorable
position for potentially some higher surge moving in than the
guidance would suggest.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...High Risk for Rip Currents until 8 PM EDT this evening for GAZ117-
     119-139-141.
SC...High Risk for Rip Currents until 8 PM EDT this evening for
     SCZ048>051.
MARINE...Small Craft Advisory until 4 PM EDT this afternoon for AMZ350-
     352.
     Small Craft Advisory until 7 PM EDT this evening for AMZ354.
     Small Craft Advisory until 11 PM EDT this evening for AMZ374.

&&

$$